The present invention relates to delivery of short messages to mobile stations and particularly to delivery of short messages in mobility-supporting packet radio networks that use a mobile communications network as an access network, to a dual-mode mobile station in a situation where the mobile station is not reachable in the packet radio network.
Mobile communications systems have been developed because there has been a need to free people to move away from fixed telephone terminals without impairing their availability. Simultaneously with the increase in the use of various data transfer services at offices, various data services have also been introduced in mobile communications systems. Lap-top computers make efficient data processing possible everywhere the user moves. Mobile communications networks offer to the user an efficient access network for mobile data transfer, thus providing access to the actual data networks. For this purpose, various new forms of data service for the present and future mobile networks are being planned. Digital mobile communications systems, such as the pan-European mobile communications system GSM (Global System for Mobile Communications), support mobile data transfer particularly well.
The General Packet Radio Service GPRS is a new service in the GSM system, and it is one of the topics of GSM Phase 2+standardization work at ETSI (European Telecommunications Standards Institute). The GPRS operating environment comprises one or more subnetwork service areas that are interconnected by a GPRS backbone network. The subnetwork comprises a number of packet data service nodes SN, termed serving GPRS support nodes (SGSN) herein, each being connected to a GSM mobile communications network (typically base station systems) so as to be able to offer a packet data service to mobile data terminal equipment via several base stations, i.e. cells. The intermediary mobile communications network offers packet-switched data transfer between the support node and the mobile data terminals. The different subnetworks for their part are connected to an external data network, e.g. a public switched data network PSPDN, via specific GPRS gateway support nodes GGSN. Hence, the GPRS service allows packet data transfer between mobile data terminals and external data networks, the GSM network serving as an access network. The GPRS network architecture is illustrated in FIG. 1.
One kind of service of mobile communications networks is short message service (SMS). This differs from voice and data services in that to send a short message, no connection from the sending party to the receiving party need to be established, as the short messages are transmitted in the form of signalling messages. Data transfer by means of short messages is limited to one message only. Short message services are asymmetric, and the transmission of a mobile-originated short message is considered a different service from the transmission of a mobile-terminated short message. In a GSM network, short messages can be received and sent even during an ongoing call, as short messages are relayed on control channels. A short message service center SM-SC is an entity delivering short messages and storing and retransmitting short messages the delivery of which has failed. All short messages pass through a short message service center SM-SC. A short message service center can receive a short message through any network for delivery to a mobile station MS. The short message service center SM-SC transfers the short message it received to a gateway mobile switching center for short message service (SMS-GMSC) for further delivery to a mobile station. An incoming short message from a mobile station is transmitted via an interworking mobile switching center for short message service (SMS-IWMSC) to a short message service center for further delivery. To provide short message service, a GPRS network has a serving GPRS support node SGSN connected to a gateway mobile switching center for short message service, SMS-GMSC, and to an interworking mobile switching center for short message service, SMS-IWMSC. Through these, a mobile station MS attached to a GPRS network can send and receive short messages on the radio channels of the GPRS.
The mobility management (MM) activities related to a GPRS subscriber are characterized by one three different MM states of the mobile station MS: Idle State, Standby State, and Ready State. Each state describes a certain level of functionality and information allocated to the mobile station MS and to the serving GPRS support node SGSN. The information sets relating to these states, which are maintained in the serving GPRS support node SGSN and in the mobile station MS, are denoted MM contexts. The context of the serving GPRS support node SGSN comprises subscriber data, such as the subscriber IMSI, TLLI, and location or routing data, etc.
In the idle state, the mobile station MS is not reachable from the point of view of the GPRS network, and the network holds no current state, location, or routing information for the mobile station MS, i.e. no MM context. If the mobile station MS is of dual mode, i.e. is capable of operating in GPRS and GSM networks, it may be in the GSM network when being in GPRS-Idle state. The mobile station MS can move from idle state to ready state by attach to the GPRS network, and from standby state or ready state to idle state by detach from the GPRS network.
In the standby and ready states, the mobile station MS is attached to the GPRS network. The ready state is the actual data transfer state in which the MS is capable of transmitting and receiving user data. The MS passes from standby state to ready state either when the GPRS network pages the mobile station or when the mobile station MS starts data transfer or signalling. The mobile station MS may remain in the ready state (for a time-out preset in a timer) even when no user data is transferred or no signalling takes place. If the mobile station is a xe2x80x98dual modexe2x80x99 mobile station and is in standby state or ready state, the paging required by circuit-switched services, e.g. a voice call to be made to the mobile station, is made through the serving support node SGSN of the GPRS network. In other words, the GSM paging is carried out as GPRS paging.
When a short message service center SM-SC receives a short message SM for delivery to a mobile station MS, the short message service center forwards it to a gateway mobile switching center for short message service, SMS-GMSC, which examines the destination MS address and requests routing information from the relevant home location register HLR. The home location register HLR of the GSM network also contains the GPRS subscriber data and routing information. The home location register HLR sends in its message the serving GPRS support node (SGSN) address of the mobile station MS or the VLR address at the mobile services switching center MSC, or both. If the HLR message contains only the MSC/VLR address, the short message is delivered normally through the GSM network. If the HLR message contains an SGSN address, the gateway mobile switching center for short message service, SMS-GMSC, forwards the short message SM to the serving GPRS support node SGSN. If the mobile station MS is attached to the network and is reachable, the serving GPRS support node SGSN transfers the short message SM to the mobile station MS.
However, the serving support node SGSN may not be able to deliver the short message SM to the mobile station MS on account of for instance the fact that the radio channel conditions are poor or the mobile station MS is detached from the GPRS network, i.e. is in idle state. The HLR is not aware of the state of the mobile station, it only knows the addresses. When the serving support node SGSN does not succeed in delivering the short message to the mobile station, the serving support node SGSN sets a flag MSNRF (=Mobile Subscriber Not Reachable Flag) indicating that the mobile station is not reachable, and sends a failure report to the SMS-GMSC.
If the routing information received from the home location register HLR does not include the MSC/VLR address, the SMS-GMSC sends to the home location register HLR a message indicating that there is a message waiting, deletes the message from its buffer, and returns a failure report to the short message service center SM-SC. The HLR updates in its registers the fields indicating that there is a short message awaiting this mobile station. If a new short message for the same mobile station arrives before the mobile station again becomes attached to the network, an attempt is made to deliver the new short message because the HLR does not know that the mobile station is not reachable. In this way, unnecessary signalling is created in the network, yet the short message cannot be delivered.
If in addition to the address of the serving support node SGSN the address of the mobile services switching center MSC/VLR was received from the home location register HLR, the gateway mobile switching center for short message service, SMS-GMSC, sends the short message SM to the mobile services switching center MSC/VLR, since the short message SM could not be delivered through the service GPRS support node SGSN.
When the mobile station is attached to both networks, the GSM paging request for the mobile station MS is sent through the serving GPRS support node SGSN. If the short message SM could not be delivered to the mobile station MS through the serving GPRS support node SGSN because the mobile station attached to the network was not reachable, i.e. did not respond to the paging request, the short message cannot be delivered through the mobile services switching center MSC/VLR either, since the mobile station MS is paged through the serving support node SGSN. On account of the failed paging, the visitor location register MSC/VLR sets a flag, Mobile Subscriber Not Reachable Flag (MSNRF), returns a failure report to the gateway mobile switching center for short message service, SMS-GMSC, which again requests the home location register HLR to update in its registers the fields indicating that a short message is awaiting this mobile station. Now an indication of the fact that the mobile station could not be reached is held in three locations. Furthermore, there is unnecessary signalling between the mobile services switching center MSC/VLR and the serving support node SGSN in connection with the paging, as the outcome is obvious.
When the mobile station again becomes reachable in the GPRS network, the SGSN sends to the home location register information on the fact that the mobile station MS is available. The same information is sent to the home location register by the MSC/VLR when the mobile station becomes reachable in the GSM network. The information sent by either the SGSN or the MSC/VLR is fully unnecessary, as the first information received by the home location register will initiate retransmission of the short message using the above routine. If the mobile station becomes reachable in the GSM network first, the GPRS is unnecessarily requested to deliver the short message first.
The above problems will also arise if the network has just recently detached the mobile station MS, i.e. transferred it to idle state, on account of the fact that the GPRS network cannot reach the mobile station, i.e. the mobile station does not respond to a paging request, for example. However, the mobile station MS considers itself as being attached to the GPRS network. In that situation, the mobile services switching center MSC/VLR attempts to contact the mobile station on the paging channel of the GSM network, but since the mobile station is still listening to the paging channel of the GPRS network, it does not detect the paging message from the other channel. The page signalling of the mobile services switching center MSC/VLR is unnecessary, since the outcome is foreseen. The short message cannot be delivered, and information about failure will produce an indication thereof in three locations, thus creating unnecessary signalling between the home location register and the respective network node.
If the mobile station MS was in idle state when an attempt was made to send the short message SM through the GPRS network, sending of the short message SM through the GSM network may be successful. The flag MSNRF will remain set in the serving network node SGSN, even though it were possible to deliver the short message SM (independently of whether the MSC/VLR was successful in delivering the short message or not). In consequence, when the MS again becomes attached to the GPRS network, the SGSN sends to the home location register a notification of this (Note MS Present) even if no short message is waiting. If the transmission of the short message SM fails, the visitor location register VLR sets a flag MSNRF and sends a report on failure of the delivery of the short message to the SMS-GMSC. Hence information is held in three locations on the fact that the mobile station could not be reached, and this will produce unnecessary signalling as stated above.
In particular, when the mobile station MS is in idle state a problem is presented by the fact that the home location register HLR only knows the most recent network addresses of the mobile station, i.e. the MSC/VLR and SGSN addresses. Hence, the home location register HLR returns both addresses in the routing information, even though the mobile station is not reachable through the GPRS. If the GPRS is the primary network, an attempt is always made to first send the message through the GPRS network, thus creating unnecessary signalling when the mobile station cannot be reached through the GPRS network.
If there is an ongoing voice call at xe2x80x98Class B mobile stationsxe2x80x99 which cannot simultaneously use packed-switched services and circuit-switched GSM services, the mobile station cannot be reached through the GPRS network. The short message can be directly delivered through the MSC/VLR as no separate paging is necessary in the GSM network when there is an established voice connection. However, when an attempt is made to deliver the short message through the serving support node SGSN, the serving support node sets a flag MSNRF as an indication of failure, even though the failure was due to the fact that the connection was suspended on account of an ongoing call. When the call is terminated, information on the fact that the mobile station MS is present in the GPRS network is unnecessarily sent to the home location register HLR.
The object of the invention is as simple an operation as possible when short messages are sent to mobile stations that can operate in two networks.
The objects of the invention are achieved with a method and a radio network which are characterized in that which is disclosed in the independent claims. The preferred embodiments of the invention are set forth in the dependent claims.
In the invention parameters controlling the network elements are inserted into signalling messages and/or information on reachability of the mobile station is provided in a subscriber database, such as a home location register.
In a preferred embodiment of the invention a subscriber database storing the subscriber data of a mobile subscriber is provided with information on whether the mobile station is reachable through the primary network or not. If the mobile station is reachable through the primary network, the subscriber database responds to a routing information request by sending an address in the primary network and optionally an address in the second network to an interrogating network element. If the mobile station is not reachable through the primary network, the subscriber database responds to a routing information request by sending an address in the secondary network to the interrogating network element. xe2x80x9cPrimary networkxe2x80x9d refers to that part of a network through which attempts to reach the mobile station are made first, in other words the primary route. xe2x80x9cSecondary networkxe2x80x9d refers to that part of a network through which attempts to reach the mobile station are made if the attempts to reach the mobile station through the primary network failed, in other words the secondary route.
Therefore, the advantage of the method and radio network of the invention is the fact that superfluous signalling is reduced when short messages are sent to mobile stations that are not reached at the precise moment of sending through the primary network.